Automatic headlight dimming apparatus



March 8, 1960 o. T. M ILVAINE 2,928,025

AUTOMATIC HEADLIGHT DIMMING APPARATUS Original Filed April 21, 1954 2Sheets-Sheet 1 I 6 24 42F J 4 0 2 38 Hull I l i 6 mvsm'oa 46 4 4 Oran 7.JWcIZI/jne ATTORNEYS ance.

United States Patent Original application April 21, 1954, Serial No.424,656,

now Patent No. 2,884,564, dated April 28, 1959. Di-

vided and this application March 16, 1959, Serial No- 6 Claims. (Cl.315-83 This application is a division of my application for AutomaticHeadlight Dimming Apparatus filed April 21, 1954, Serial No. 424,565,now Patent No. 2,884,564, granted April 28, {1959.

'lh'isinvention relates to automatic headlight dimming apparatus foreffecting the automatic control of multi-beam headlights on vehicles.

Prior to the present invention, many attempts have been made to providepractical apparatus for automatically dimming the headlights ofautomobiles upon the approach of another vehicle from the oppositedirection. Such apparatus isfinthded to relieve the driver of theobligation-to dim the headlights, and in this manner to increase hiscomfort andalso to reducethe' likelihood that the headlights tvill notbe dimmed onfcerta'in occasions through negligence.

The prior apparatus has utilized semi/muons photoelectric cell mountedon the automobile just behind the windshield or in the middle of thegrill, to receive light from oncoming vehicles, and a relay positionedsomewhere under the hood of the automobile and arranged to be actuatedin response to action of the photoelectric cell; The relay controls theheadlight circuit, and. its

actuation controls the bright and dim circuits of the headlights.Amplifiers are usually included in the system between the photoelectriccell and the relay'to'amplify the signals sufficiently for the properoperation of therelay. Some systems utilize a lens or combination oflenses, positioned in front of the photoelectric cell to collect thelight emanating from the approaching vehi 1e and focus it upon thephotoelectric cell.

All of the prior art efforts have been subject to certain 2,923,025Patented Mar. 8, 1950 ICC cidence of the efiective light rays, preventsactuation of the photoelectric cell by the rays emanating from theheadlights of a vehicle approaching from around a curve. *It frequentlyhappens in the use of the lens system of this type that the dimming ofthe lights does not occur until the vehicles are very close to eachother, and dangerous blinding of the approaching driver results.

-In' the priorart detectors having'no focusing lenses, there isalmost-no discrimination between the various light sources. Thephotoelectric cells are actuated by such extraneous light sources asstreet lamps, highway signs, and even the glare of the road surface. Theunnecessary dimming operations thus produced are annoymgh'nd alsodangerous to some extent in that they greatly reduce the length of theilluminated stretch of roadway in front of'the vehicle.

The apparatus of the present invention embodies a number of featureswhich cooperate to overcome effectively all of these dilficulties whicharise in connection with the prior art apparatus. Instead of a separatedetector unit mounted behind the windshield or in the middle of thegrill of the automobilefl have combined the detector with a conventionalheadlight and aparking light and turn indicator to form an illuminationunit. By forming these elements as a single unit whichcan be installedin a single operation, the cost is materially reduced. I.--An0therfeature which maybe used, if desirech-to lower the cost of installingand maintaining the automatic dimming" equipment, is the elimination ofa separate relay unit from the system. This is accomplished by utilizinglight-actuated switching means in place of the conventionalphotoelectric cell in the detector.

The novel lightac'tuated switching means which may be with thisinvention, is in the form of an electron discharge tube having acathode, a light-sensitive grid, an anode, a pair of fixed contacts anda movable contact.

, The cathode is formed so as to be distortable upon changes in thetemperature thereof and is'connected to the movable contact. Lightfalling upon the light-sensitiv'e grid causesithe emission of electronstherefrom, and

practical difiicult'ies, which are overcome by the present i invention.I

One such difiiculty arises in connection'with the mounting of thephotoelectric cell detector unit on the vehicle. If the unit ispositioned behind the windshield, itobstructs the vision of the driverand is unsightly in appear- If it is mounted in the middle of the grill,the cost of installation is too great, for in this case, it is necessaryto form an extra opening in the body of the vehicle during themanufacture thereof and to include an extra operation in the finalassembling'process.

Furthermore, the detectors used heretofore were not suflicientlyreliable in operation. In order to be useful at all, apparatus of thistype must be almost perfect with respect to its reliability. The drivercannot have confidence in a system that works onl'y-partof the time.

The lenses are quite satisfactory on straight; level roads, and serve toprovide a measure of discrimination as between light sources becausethey magnify the intensity of tory when the automobile is travellingalong a roadwith the movement of these electrons through the gas withwhich the tube is filled results in the ionization of the gasand firingof'the tube. The current flow between the cathode and the anode whilethe tube is firing causes the cathode to heat up and be distortedappreciably. The movement of the cathode thereby is utilized to move onecontact from engagement with one of the fixed contacts -into engagementwith the other of the fixed contacts. The contacts are in the bright anddim circuits of the headlights and, consequently, the light-actuatedswitching apparatus of this invention accomplishes the dimming oftheheadlights directly and without the necessity for using a relay.

The detector that may be used according to this invention is made morereliable by providingthe detector .with a reflector element which willcollect light from the headlights of the approaching vehicle and focusit upon the light-sensitive element of the detector. The reflector ismuch more satisfactory as a light collecting device than the'lenssystems used heretofore, because it permits :the collection of lightfrom sources disposed at fairly large angles in the horizontal planefromits axis. This means that the light from a vehicle approaching fromvarounda curve will be received by the reflecto. and divrecterl to thelight-sensitive element to actuate it.-

Proper discrimination as between various light sources is attained by acombination of features. The front end .portion of the refiectoris.preferably much wider than it is high so that the angle through whichlight may. be admitted is greater in the horizontal plane than in thevertical plane. This helps to prevent actuation of the detector by suchlight sources as street lamps and the glare of the road surface. 7

Further and more effective restriction of the vertical angle ofadmittance of light rays to the detector is accomplished by theprovision of a louver panel in front of the reflector. This louver panelincludes horizontally disposed louver strips of such width and spacingas to prevent the entrance of light from sources disposed substantiallyabove and below the. horizontal axis of the detector. The louver panelmay also include, if desired, vertical louver strips on one or bothsides of the detector to restrict the collection of light from sourcesdisposed at wide angles in the horizontal plane.

The effect of light sources located above and below the horizontal axisof the detector is further reduced by utilizing a light-sensitiveelement which is in the form of a thin plate disposed with its faces invertical planes. It will be apparent that this arrangement accentuatesthe effectiveness of light approaching substantially horizontally, whileminimizing the effectiveness of light approaching from other angles.

A more complete understanding of this invention and its many advantageswill become apparent from the following detailed description whenconsidered in connection with the accompanying drawings in which:

Fig. l is a front elevation view at the left side of an automobile,showing the detector unit of this invention applied thereto;

Fig. 2 is a detail vertical sectional view taken along line 22 in Fig.1, showing one form of detector according to this invention and themeans for attaching the combination unit to the body of the vehicle;

Fig. 3 is. a detail horizontal sectional view taken along line 3-3 inFig. 2; v

Fig. 4 is a perspective view of one form of photoelectric cell which maybe used in the detector;

Fig. 5 is a front elevational view of another form of detector that maybe used with the present invention;

Fig. 6 is a vertical sectional view therethrough taken on the line 66 inFig. 5;

Fig. 7 is a side elevational view of a light-actuatedv switching devicethat may be used in accordance with this invention;

Fig. 8 is a circuit diagram, illustrating. the useof the device shown inFig. 7 in controlling the dimming of automobile headlights;

Fig. 9 is a section similar to Fig. 6, but shows another modification;and

Fig. 10 is a diagram of a circuit for use with the de tector unit ofFig. 9.

Referring more particularly to the drawings, Fig. 1 shows theillumination unit 4 of an automobile, designated generally by thenumeral 2. Most of the automobile has been broken away in this view,because it was according to this invention, are shown in Fig. 2. Alightsensitive tube 20 is mounted in a socket 22, disposed at the rearend of a reflector 24 attached by brackets, not shown, to theillumination unit frame 6.

One form of light-sensitive tube 20 that may be used, is illustrated inFig. 4. This includes a pair of anodes 26 disposed on opposite sides ofa light-sensitive cathode 27. The cathode 27 is in the form of a thinplate. The tube is preferably plugged into the socket 22 with the facesof the cathode 27 disposed in vertical planes.

Gther types of tubes may be used, however, if desired. For example, thetube shown in Fig. 7 or in my prior Patent No. 2,307,697, has advantageswhich may justify use thereof in place of the tube construction shown inFig. 4.

The inner surface of the reflector 24 is preferably in the shape of aparaboloid, at 28, with the light-sensitive element of the photoelectrictube 20 at its focal point. As shown in Fig. 2, the parabolic surface 28is at the rear portion of the reflector with a forward portion 30,having substantially flat top and bottom walls, sloping away from thereflector axis at smaller angles than the side walls. The side walls ofthis forward portion 30 of the light-reflecting surface are preferablycontinuations of the parabolic rear portion 28.

The reflector 24 should be large enough to admit sufficient light forthe operation of the photoelectric tube, but it should not be so largeas to give an unsightly appearance to the illumination unit. A range ofsuitable sizes would be from one and one-half to seven inches, as,measured along the horizontal line connecting the centers of the forwardedges of the walls of the reflector, as viewed in Fig. 1.

Near the front end of the reflector 24, the inner sur face is providedwith a shoulder 36, against which the frame portion 38 of the louverpanel is positioned in this embodiment. By reason of the elongated shapeof the front end of the reflector 24, as viewed in Fig. l, the louverpanel is necessarily oriented as to the vertical and horizontaldirections when it is inserted into the reflector to bear against theshoulder 36. The louver panel includes horizontal louver strips 40 andvertical louver strips 42.

All of the strips should be painted black on both sides, or otherwisetreated, to prevent the reflection of light from their surfaces so thatpractically all of the light going to the reflector 24 must passdirectly through the spaces between the louver strips- The width andrelative spacing of the louver strip elements may be varied as desiredto control the angle of admission of light to the reflector. Thearrangement shown in Figs. 2 and 3 is merely an example of variousdispositions which may be not necessary in order to illustrate therelationship between the illumination unit and the automobile. Theillumination unit 4 comprises a frame 6, the front surface of which maybe suitably treated to present a desirable appearance. Mounted in theframe 6 are a headlight 8 of conventional multi-beam construction, acombination parking light and turn indicator 10, also of conventionalconstruction, and adetector 12.

The illumination unit 4 may be attached to the body of the vehicle inany suitable manner, as by a number used for particular locations.

The louver panel is maintained in position against the shoulder 36 bymeans of a clear, transparent cover plate 44, mounted at the outer endof the reflector 24, as by means of a holding ring 46, the rear end ofwhich is fastened to the reflector 24 by set screws or other fasteningdevices, not illustrated. The cover plate 44 serves to prevent theentrance of dirt, insects and other foreign objects into the reflector.

It will be seen that the detector ofthis invention in cludes a number offeatures which cooperate to make the operation thereof more reliable.The concave light reflecting surface 28 is shaped so as to collect thelight falling upon the detector and to direct it onto the lightsensitive element 27 of the tube 25). The vertical disof bolts, one ofwhich is shown at 14 in Fig. 2. These 7 bolts pass through flange-likeears 16, projecting rearwardly from the frame 6, and through similarears projecting rearwardly from the edge of the opening in the body ofthe automobile. There may be a number of bolts 14, and these assure therigid attachment of the illumination unit 4 to the vehicle body.

The details of construction of one form of detector,

position of the light-sensitive element 27 in the detector minimizes theeffects produced by light falling upon the tube 20 from aboveor below,and thereby reduces the likelihood of actuation of the detector by lightfrom street lamps or from the road surface.

The relatively small slope of the top and bottom walls of the forwardportion 30 of the light-reflecting surface .28 permits the verticaldimension of the forward end of the reflector to be substantially lessthan its horizontal dimension. This shape serves to reduce the amount ofto restrict the angle of entrance of light into the reflector.

to any desired range. Ordinarily, it is preferable, that the horizontallouver strips 40 be relatively wide and closely spaced so as to restrictthe light entering the reflector to an angle approaching the horizontal.However, these dimensions must be determined carefully, considering theconditions to be met in use and the terrain to be encountered. Thevertical louver strips 42 are of lesser importance and in some instancesthey could be omitted entirely. They must not beailowed to interferewith the collection of light from. vehicles approaching from aroundcurves.

Figs. and dillustrate a modification of the detector of this invention,designated generally at 48, which is similar in many respects to theembodiment already described. Here, however, the entire light-reflectingsurfaceSi) of the reflector 52 is shaped as a. paraboloid and theentrance end of the reflector is circular, as seen in Fig. 5. A.reflector of this shape has considerably greater light-gathering powerthan. one of theshape shown in Figs. 1 and 2, and the use of. such areflector may be preferred in some instances. The diameter of the en- Insecuringthe'louver panel 54 to the reflector 52, it is desirable toprovide the frame. of the louver panel with a rearwardl'y extendingkey56 engageable in a slot 58 in the shoulder 66, formed on the innersurface of the reflector. The location of the key 56 in the slot 58assures the directional orientation of the louver elements. The louverpanel 54' is shown as having only horizontal louver strips, but it willbe understood that vertical strips may also be provided, if desired. Theglass plate 62 and the fastening ring 64 are similar to thecorresponding elements shown in Fig. 2, except for their shape.-

Although the photoelectric tube used in-the embodiment illustrated inFigs. 5 and 6 may be of the" type shown in Fig. 4, the vertical plateform of light-sensitive elementis not essential with this form ofreflector. For example, a photothyratron tube such as that disclosed inmy Patent No. 2,307 ,697, may be employed to actuate a switching relaydirectly, without requiring amplification of the signal from thelight-sensitive cell. Moreover, light-actuated switching means, such asthat shown in Fig. 7, might be used to eliminate both the amplifier andthe switching relay. 7

Fig. 7 shows one form of lightactuated switching means that may be usedwith the present invention. This includes a gas-filled envelope 76having a transparent window, a base 72, and a plurality of terminal pins74, adapted for insertion in: a socket to provide the electricalconnections for the various elements inside the envelope 70. An element77 serves as an electronic tube cathode which cooperates with, an anode76, protrudingfrom a supporting stud 78, and a loop grid element 80encircling the anode 76 and supported by a stud 82 and wire 83.

'The wire 83 need not be connected to any oi the terit serves only as asupport for grid. element 80 is coated with a light-sensitive material,

such as caesiurmso as to form. a photo-cathode. In the present tube, theelement servesfas a control element V 6 or grid tocontrol the currentflow between the electiohic cathode77 and the anode 76.

When light falls on the photo-cathode 80, electrons are emitted from thesurface thereof and directed toward the anode 76; The movement of theelectrons through the gas causes ionization of the gas and firing of thetube. cathode 77, which occurs when the resistance between theseelements is lowered by the ionization of the gas, causes the electroniccathode 77 to be heated by the cathode glow. .The increase intemperature of the bimetallic electronic cathode 77 produces adeformation, which is utilized in a manner explained below, toaccomplish the switching operation.

In another portion of the tube is located a pair of relatively fixedcontacts 84 and 86. These are alternately engaged by a movable contactmember 88, pivoted as at 90. The deformation of the electronic cathode77 is translated into motion. of the movable contact 88, by means of an.insulated connector rod 92 attached to the upper end of the electroniccathode 77 and extending across the tube to a point above the movablecontact 88. The end of the connector rod 92 is coupled to the movablecontact $8 by means of a compression spring 94, the ends of which areattached, respectively, to the connector rod. 2 andto themovable contact88. l

As long as the bi-metallic member 77 is cool, the'axis of thecompression spring 94 is inclined in one direction with respect to thevertical, and the movable contact 88 is caused to engage one of thefixed contacts, as*84. When the tube fires, and the temperature ofthe'bi-metallic member 77 rises, the bi-inetallic member bends andshifts the connector rod 92 in the direction or the arrow 96 in Fig. 7,.to change the inclination of the com- .83 into engagement with thefixed contact 84.

Certain variations in the construction of this switching apparatus willbe apparent. For example, the deformation used to bring about theswitching of the contacts might be the linear expansion of a. brassstrip rather than the bending of a bi-metallic element. Also, the heatdistortabl'e member could be the movable contact. In this case, themovement back and forth between the. two fixed contacts would berelatively slow, however, as the movement would correspond to the rateof change of the temperature of the member. Ordinarily, this type ofaction is not as desirable as the snap action achieved by the ructureillustrated in Fig. 7, but there may be situations in which it would bedesirable.

It will also be apparent that. the principles of the switching apparatusof this invention are not restricted to the inclusion in the tube of alight-sensitiveelement. The firing of the tube might be in response 'tocontrol signal potentials impressed upon a conventional grid instead ofin response to the incidence of light upon a light-sensitive element.Switching apparatus of this type might be used in conventional dimmingsystems in place of the usual amplifier and relay elements, the signalsfrom the photoelectric cell being transmitted to the grid element.

Fig. 8 illustrates the use of the light-actuated switch ing apparatus ofFig. 7 in the dimming of automobile headlights. The conventionalautomobile battery 102 is connected through conventional vibrator,transformer, rectifier, and filter apparatus to the anode 76 of the tube79. The rectifier and filter might be omitted as the tube will operateon alternating current, as well. Of course, the reason for providing thevibrator and associated equipment is to raise the voltage of the batteryto a suificient value, as from 100 to 200 volts, forexample, foroperating the tube. The fixed contact 84 isin circuit The current fiowbetween the anode and electronic with the bright filaments 106 of theheadlights of the automobile and, normally, the engagement of themovable contact 88 with the fixed contact 84 completes the circuit fromthe battery 102 through these bright filaments 106. Movement of themovable contact 88 into engagement with the fixed contact 86 closes thecircuit from the battery 102 through the dim filaments 108 of theheadlights. This dimming of the headlights occurs automatically inresponse to the reception of light from an oncoming vehicle falling orbeing reflected onto the photo-cathode 80, as will be apparent from theabove discussion.

It is pointed out that the timing of the switching operations in thecircuit of Fig. 8 is novel and highly advantageous. The dimming of theheadlights does not occur immediately upon the reception of light fromthe/headlights of an approaching vehicle but is delayed for a short timewhile the cathode 77 heats up sufficiently to snap the movable contact88 into engagement with the fixed contact 86 in the dim circuit. Thisdelay has a duration of from two-tenths to four-tenths of a second andcovers the period when the light falling on the lightsensitive element80 is of borderline intensity to prevent flashing of the headlights backand forth between bright and dim.

After the light from an approaching vehicle goes oi the light-sensitiveelement 80, there will be another delay period before the return of theheadlights to bright, and momentary removal of the light from thedetector, such as might occur in a meeting situation on a hill, is noteffective to return the lights to bright. The delay circuit illustratedin Fig. will provide for this delay.

In the embodiment of the invention shown in Fig. 9, the reflector 110and associated parts may be the same as those described above inconnection with Fig. 2 or Fig. 6, and the photoelectric cell 112 may beof any of the types already mentioned. This embodiment differs fromthose described in that a space discharge tube 114, containing a rareelement gas, such as argon, neon, xenon, etc. is mounted in a socket 116on the reflector 110. When this tube is illuminated, the light therefromfalls on the photoelectric cell 112 to actuate it.

A circuit in which the structure of Fig. 9 is utilized to produce noveldelay eifects is illustrated in Fig. 10. The automobile battery 102 isconnected to a conventional vibrator 118 and a transformer 120, to stepup the voltage to about 500 volts. A relay 122 is normally energizedfrom the high voltage winding of the transformer 120 through the pentodesection of a triode-pentode tube 124, but the pentode section of thetube 124 will be blocked and the relay 122 deenergized when light fallson the light-responsive device 112, such as a conventional photoelectriccell.

A movable contact 128 on the relay 122 is connected to the battery 102to supply current alternately to the bright filaments 106 and the dimfilaments 108 of the headlights through fixed contacts 130 and 132,respectively. The movable contact 128 is biased toward engagement withthe fixed contact 132 as by a spring 134 so that the dim filaments 108will be energized whenever the relay 122 is not exerting suflicientforce to overcome the bias of the movable contact 128. With thisarrangement the dim filaments 108 will be energized initially while thecontrol circuit is warming up, and then the control circuit willregulate the energization of the filaments 106 and 108.

In order to prevent deenergization of the relay 122 by quick flashes oflight, a condenser 136 is connected across its coil as shown. Thiscondenser is of such size as to hold the relay in the energizedcondition for an interval of time, such as from about two-tenths of asecond to one second, after the pentode section of the tube 124 isblocked. It will be seen that this interval corresponds to the intervalrequired for the heating up of the element 77 in the embodimentillustrated in Fig. 7.

The relay 122 is provided with another movable contact 138 connected toa condenser 140 and arranged to cooperate with a pair of fixed contacts142 and 144. The movable contact-138 is biased by the spring 134 towardengagement with the fixed contact 142 to complete a circuit whichincludes the condenser 140 and the neon tube 114 (Fig. 9). Uponenergization of the relay 122, however, the movable contact 138 moves toengage the fixed contact 144. The fixed contact 144 is connected to thehigh voltage winding of v the transformer through a rectifier 146.

In operation, the condenser is charged each time the relay 122 isenergized and is discharged through the neon tube 114 when the relay 122is deenergized. During the interval required for the discharge of thecondenser 140, the neon tube 114 will be illuminated so as to assurecontinued operation of the photo-electric cell 112. The size of thecondenser 140 is such that this interval, preferably, will be from threeto fifteen seconds. When the condenser 140 is fully discharged, the neontube 114 will be deenergized, and if no other light is falling on thecell 112, the relay 122 will be energized again to switch the headlightsfrom dim to bright and instantly recharge the condenser 140.

While the neon tube 114 is illuminated, removal from the cell 112 of thelight coming from the headlights of an approaching vehicle, such asmight occur in a meeting situation on a hill or on a curve, will not beeffective to return the lights to bright. This is an important featurebecause it prevents accidental blinding of the approach- .ing driver dueto terrain irregularities.

It will be understood that a neon tube and condenser may be, andpreferably are, associated with the lightactuated switching apparatus ofFig. 7 to provide a delay period after the switching of the headlightsto dim during which they may be returned to bright. These elements havebeen omitted from the circuit diagram of Fig. 8 in the interests ofsimplicity and clarity, but persons skilled in the art will have nodifficulty in visualizing the necessary circuit connections.

The heating of the cathode will provide perhaps .2 to .4 second, but alonger time is not desirable here. This is sufiicient to prevent quickflashes of light from operating the unit, and in the case of a standardlight-responsive cell and amplifier, this delay is secured by thecondenser 136 across the relay. The neon light 114 provides the 3 to 15seconds delay that has been found desirable after the unit first goes todim. This delay then expires and the light from the oncoming car holdsit dim. In this way, as soon as the car passes, the lights are backbright at once, which is quite important, since this is the time thatthe drivers eyes are still blinded and the bright lights help to recoverfaster. If the cathode had to cool down, this would cause the lights tobe dim after the car passed.

These delays are quite important to a successful dimmer, and the propersequence of them. When light strikes the dimmer, there will be a .2 to1.0 second delay before the dimmer operates. After the dimmer operates,there will be a 3 to 15 seconds delay beforeit will re turn, even thoughthe light is removed. There will be instant return, or practically so,to bright after light is removed from the dimmer.

Since various modifications of this invention will be apparent topersons skilled in the art, the foregoing disclosure of specificembodiments of the invention is to be considered as exemplary only andthe scope of the invention is to be ascertained from the claims whichfollow.

I claim:

1. Apparatus for automatically dimming a vehicle headlight upon theapproach of another lighted vehicle from the opposite directioncomprising a photoelectric cell and a reflector associated therewithhaving a concave light-reflecting surface for collecting light emittedby the approaching vehicle and directing it onto said photoelectriccell, said light-reflecting surface including a rear portion shaped as aparaboloid disposed so that said cell is near the focal point thereofand a forward portion having curved side walls forming continuations ofsaid paraboloid and top and bottom walls sloping away from the reflectoraxis less than said side walls, whereby the collection of light fromsources above and below the axis of said reflecting surface is minimizedwithout materially affecting the collection of light from sourcesdisposed at angles in the horizontal plane from said axis.

2. Apparatus for automatically dimming a vehicle headlight upon theapproach of another lighted vehicle from the opposite directioncomprising a photoelectric cell including a light-sensitive elementshaped as a thin strip having faces of substantial width and length andmeans for mounting said photoelectric cell on the vehicle with the facesof the light-sensitive element disposed vertically so as to minimize theeffect on said element of light approaching said cell from sourceslocated substantially above and below the cell.

3. Apparatus for automatically dimming a vehicle headlight upon theapproach of another lighted vehicle from the opposite directioncomprising a photoelectric cell including a light-sensitive elementshaped as a thin strip having faces of substantial width and length, areflector having a light-reflecting surface disposed around saidphotoelectric cell for collecting light emitted by the approachingvehicle and directing it onto said cell, said light-reflecting surfaceincluding a portion disposed forwardly of said cell having a pair ofopposed walls spaced a short distance apart and a pair of opposedconcave walls spaced a larger distance apalt, and means for mountingsaid photoelectric cell and said reflector on said vehicle with thefaces of said light-sensitive element and said concave wall disposedvertically, whereby the collection of light from extraneous sourcesabove and below said reflector and the effect of light from said sourceon said light-sensitive element are minimized.

4. In combination with a vehicle headlight having a dim circuit and abright circuit, light-sensitive electrical switching apparatus forcausing said bright circuit to be deencrgized and said dim circuitenergized upon the approach of another lighted vehicle travelling in theopposite direction comprising a gas-filled bulb enclosing a bimetalliccathode, a photo-grid, an anode spaced from said cathode, circuit meansfor applying a potential across 10 said anode and cathode sufiicient tocause the passage of electrons from said photo-grid to said anode whenlight falls on said photo grid with consequent ionization of said gasand thereafter to cause the flow of current between said anode and saidcathode whereby said hi metallic cathode is heated and caused to deformin response to the incidence of light upon said photo-grid, a firstfixed contact in said bright circuit, a second fixed contact in said dimcircuit, a movable contact movable between said first and second fixedcontacts, a compression spring connected with said movable contact anddisposed with its axis generally transverse to the direction of movementof said contact, and insulating means connecting said spring with saidbimetallic cathode for causing the axis of said spring to shift relativeto said movable contact upon deformation of said bimetallic cathode tocause said movable contact to snap back and forth between said first andsecond fixed contacts under the control of said cathode to alternatelyenergize said bright and dim circuits 5. Electrical switching apparatuscomprising a gasfilled electron tube, an expansible cathode, aphoto-grid, an anode spaced from said grid, and a spring biased contactswitch connected to the cathode, whereby actuation of the grid by lightwill cause the tube to conduct thereby causing the expansible cathode toheat, to change its shape, and to activate the contact switch to snap itfrom one position to another.

6. Light actuated electrical switching apparatus comprising a gas-filledelectron tube, an element in said tube formed so that its configurationchanges appreciably upon change in its temperature, a fixed contact insaid tube, and a cooperating movable contact in said tube movable bysaid element relative to said fixed contact in response to temperaturechanges in said element accompanying the ionization and de-ionization ofsaid gas in the course of the operation of said tube.

References Cited in the file of this patent UNITED STATES PATENTS494,765 Tyler Apr. 4, 1893 1,747,648 Ruben Feb. 18, 1930 2,132,987Hopkins Dec. 12, 1939 2,571,981 Wensel Oct. 16, 1951 2,807,752 McIlvaineSept. 24, 1957

